Processing station for an electrophotographic information printer

ABSTRACT

A processing station in an electrophotographic information printer, comprising at least one mechanically movable, preferably rotatable member (19) comprises as a drive means for said member (19) an electronic stepping motor (38) which is supplied with drive pulses of a predetermined pulse number and frequency from a motor drive unit (39) which is connected with a program-controlled control unit (35) for operating the stepping motor (38) in an operational sequence for the information printer.

The invention relates to a processing station for an electrophotographicinformation printer including a xerographic system.

Information printers for use in connection with data and word processingsystems may essentially be divided into two main categories. In onecategory, the transformation of electronic character information intoprinted information on a paper sheet is performed by means of writingdevices operating with mechanical impact in connection with carbonribbons in the same way as known from manually operated typewriters.Printers of this category comprising, inter alia, matrix printers anddaisy-wheel printers have a relatively low speed and have appeared inpractice to be rather sensitive in mechanical respects and, in addition,in respect of reproduction performance they are limited to a definitenumber of characters.

The other main category operates without mechanical impact and comprisesmainly so-called jet-ink printers and machines operating with anelectrophotographic transfer of information in connection with thexerographic reproduction technology known from usual copying machines.In particular, machines of the latter kind comprise laser printers, inwhich an electrostatically latent image is formed on a photoconductor bymeans of a controlled laser beam. Due to the very high printing speedand the fact that in respect of information reproduction they are notlimited to a definite number of e.g. alpha-numerical characters definede.g. by the characters on a daisy-wheel, these machines are findingincreasing use.

The electrostatically latent image is developed by means of toner powderand is transferred to a paper sheet and affixed thereto under use of thewell-known xerographic technology.

Since the starting point for such information printers has been thetechnology known from usual xerographic copying machines, these machinesare designed, in practice, in the same way as conventional copyingmachines with a number of processing stations comprising

a photoconductor station with an electrostatically chargeable, movablephotoconductor;

an imaging station in optical information transfer relation to thephotoconductor station;

a developer station with a toner development system and a toner cleaningstation arranged in operative relation to the photoconductor station;

an image transfer station arranged in operative relation to thephotoconductor station for transferring a toner image on thephotoconductor to a sheet-shaped printing material;

a fixation station for permanently affixing a toner image to theprinting material; and

advancing stations arranged between the image transfer station andbetween the latter and the fixation station, respectively.

As a driving means, use is made in such machines of a single motor forseveral mechanically movable, usually rotatable members, such asphotoconductor drum, sheet advancing rollers, and toner transportmechanisms, complicated transmission means being often used between thedriving means and the individual rotating members or between the lattermutually.

As in the case of conventional copying machines, this machine designmakes maintenance heavily complicated and often results in interruptionsof operation of long duration, since irregularities in the mechanicalfunctions usually require a difficult and time-consuming repairinvolving replacement and/or adjustment of components which arefrequently difficult to access.

Whereas these disadvantages may usually be tolerated in connection withconventional reproduction equipment, they will often be consideredunacceptable in connection with data and word processing systems and inthis field attempts are made to circumvent them by use of spareequipment with the costs resulting therefrom.

Due to the high printing speed of non-impact information printers of thexerographic type, the sheet supply device which picks up sheetsindividually from a sheet supply and advances them into a sheetadvancing path leading to the image transfer station must be able toperform its functions quickly and reliably in an exactly timedrelationship to the rotation of the xerographic device so that a sheetadvanced from the sheet supply will arrive at the image transfer stationin synchronism with the powder image formed on the xerographic device.

Conventional driving means and transmission devices as mentioned abovewill normally put restrictions in the structural design of the sheetsupply device and its location in the machine frame with respect to thesingle drive motor and the image transfer station.

It is the object of the invention to provide a new design of aninformation printer of the kind mentioned above breaking with theconventional technical structure of electrophotographic machines througha very simple structural design resulting in a higher level of precisionin the control of the mechanical movement operations, a considerablysimpler maintenance and an increased flexibility with respect to machinestructure and function.

According to the invention an electrophotographic information printer isprovided with a xerographic reproduction system including a sheet supplywith associated sheet feeding means for feeding individual sheets to asheet advancing path, a movable photoconductor with an associated imagetransfer device arranged at said sheet advancing path for transferring atoner image developed on said photoconductor to a sheet advanced alongsaid sheet advancing path and a further sheet advancing device forconveying sheets from said image transfer device to a fixation device,said sheet supply device with associated sheet feeding means, said photoconductor and said further sheet advancing device forming individualreplaceable first, second and third sheet processing modules,respectively, at least two of said first, second and third modules eachcomprising an individual drive means in the form of an electronicstepping motor which is mechanically coupled to at least one rotatablemember within said module, a device for selectively supplying drivepulses of a predetermined pulse number and pulse frequency to saidstepping motors within each of said at least two modules being connectedto a program-controlled control unit for operating said stepping motorsin an operational sequence for said information printer.

As a result of this design of the sheet supply, the photoconductor unitand said further sheet advancing device as separate, individuallyreplaceable modules, which may be inserted into supporting means in aframe structure of a machine housing in such a way that they may beindividually removed from and inserted into the machine casing withoutinterfering with the remaining modules, repair of a mechanicalmalfunction may take place by a simple and quick replacement operation.

As a result of the use of an electronic stepping motor as a drivingmeans in each of these modules mechanical transmissions between themodules mutually or from the modules to a common motor is not in use,which also makes a major contribution to make the information printermore easy to service by improving the accessibility to all parts of themachine.

Operation of the stepping motor in a processing station is initiated bycontrol from a common control unit which preferably comprises a microprocessor programmed to initiate the mechanical movement functions insaid modules as well as other operations in a working cycle, such ascharging and decharging of the photoconductor by means of corona wiresat the right moments in a sequence of operations. By this control, thestepping motor will be individually supplied with pulse sequences whichwithout any need for feed-back or position-sensing causes it to rotatewith a prescribed speed or a prescribed angular turn. As a resultthereof, an essentially more accurate control is obtained than possiblefor conventional driving means in xerographic machines, since theoperation of the driving means is linked and directly governed by themain control unit. Thereby, an essentially improved accuracy withrespect to the operational cooperation between the sheet feeding means,the photoconductor and the further sheet advancer means is obtained.

In an information printer according to the invention, the furtheradvantage is obtained that operation parameters for the movement andother operational functions of the station may be changed individuallyby simple reprogramming of the control unit. Thereby, it is madepossible for a given machine to make changes in the individual stationsformed as modules concurrently with the development of technologywithout any need of changes in other parts of the machine.

In the following, the invention will be explained in further detail withreference to the accompanying drawings, in which

FIG. 1 is a perspective view of an information printer according to theinvention;

FIG. 2 illustrates the connection of a number of module units to acoupling unit;

FIG. 3 is a block diagram illustrating the control of a stepping motorin an individual processing station;

FIGS. 4 and 5 are function and pulse diagrams for explaining the controlof the stepping motor;

FIG. 6 shows the design of sheet cassette modules; and

FIG. 7 shows a part of FIG. 3 at a larger scale.

In the embodiment shown in FIG. 1, the machine casing of the informationprinter, the side walls of which are removed, comprises a box-like framestructure having vertical and horizontal frame members 1 and 2, to whichsupporting means, not illustrated, are secured in the form e.g. ofsliding rails for the arrangement of the processing station designed asseparate individually replaceable modules.

An imaging module 3, to which electronic information signal codes aresupplied, is constituted in this embodiment by an electronicallycontrolled line-scanning electro-optical device having a scanningdirection, as shown by a light exit slit 4.

Such an electro-optical device may be constituted e.g. by a cathode raytube having a high brilliance whereby the advantage is obtained that theimaging unit unlike other scanning imaging devices does not comprisemechanically moved scanning members.

However, also devices of the latter kind employing e.g. a controlledlaser beam may be used.

An optical module 5, which may be of a design known per se includingmirrors 6 and 7, causes light information from the imaging module 3 tobe focused onto a movable photoconductor 8 in a photoconductor module 9.

The photoconductor 8 may consist in a known manner of a rotating drumhaving a photoconductive coating.

In an operative relation to the photoconductor 8, a developer module 10is arranged having a toner supply 11 and a rotating magnetic brush 12for transferring toner powder onto the photoconductor for development ofa latent electrostatic image thereon.

Moreover, there is arranged in association with the photoconductor 8 atoner cleaning and recycling module 13, which is connected with thedeveloper module 10 through a duct 14.

The module 13 is arranged above the module 10 with an intermediateseparation allowing for passage of the optical information from themodule 5 onto the photoconductor 8.

In the module 13 or in connection therewith, an electrostatic chargingmeans in the form of a corona wire 15 is arranged.

In order to decharge the photoconductor 8 for the purpose oftransferring a powder image developped by means of the developer module10 onto a sheet of printing material, an image transferring module 16having a corona wire is provided.

In order to advance the sheet material from a sheet supply to imagetransfer contact with the photoconductor 8, a first advancing module 17is provided, which is designed in the embodiment shown as a sheetfeeding unit with a collecting roller 18 and sheet advancing rollerscomprising a driven roller 19 and a number of pressure rollers 20. Thesheet feeding unit is built into a sheet cassette, the detailed designof which will appear from the following.

Subsequent to the image transfer, the information carrying sheet isstripped from the photoconductor 8 and transferred to a second sheetadvancing module 21. By means of this module, which may comprise e.g. anumber of belts 22, the sheet is transferred to a fixation module 23 forpermanently affixing the transferred powder image to the sheet.

The module 23 may be either of the hot fusing or the pressure fixationtype.

In the embodiment in FIG. 1 all the modules 3, 5, 9, 10, 13, 16, 17, 21,and 23 may be designed as separate, individually replaceable modules,and those modules comprising mechanically movable parts, in the exampleshown rotating elements, i.e. all the above mentioned modules with theexception of the modules 3, 5, and 16, may each comprise as anindependent drive means an electronic stepping motor.

As is apparent from FIG. 2 showing the modules 10, 21, ans 23, each ofthe stepping motors 24, 25, and 26 associated therewith are built-ininto its own module in the embodiment shown, whereby an optimumflexibility in respect of the machine design is obtained.

For each module, the only external connection consists of a plug 27, 28,and 29, respectively, for direct insertion into terminal connections 30,31, and 32 of a coupling unit 33, which may have the same design as icircuit card. The terminal connections 30, 31, and 32 are connected, onone hand, to a power supply unit 34 for supplying operational voltagesto the modules and, on the other hand, to a common program-controlledcontrol unit 35. The plugs may be fixed with respect to the individualmodules as shown, or they may be connected therewith through relativelyshort wire conductors, for instance a multi-conductor flat cable.

The units 34 and 35 are arranged together with an interface module 36 onthe side of the plate-shaped coupling unit 33 opposite the modules 10,21, and 23.

The interface module 36 serves in a known manner as a matching devicebetween the imaging module 3 and an electronic data or word processingsystem in accordance with the standard protocol applicable therefor.

FIG. 3 shows schematically the features of the design of a singleprocessing station, for instance the above mentioned sheet feeding unithaving a pair of rollers 19, 20, which are essential to the invention.

The driven roller 19 is connected through a toothed belt transmission 37with the output shaft of an electronic stepping motor 38 which issupplied with drive pulses from a motor drive unit 39. In a moduledesign, the motor drive unit 39 may be arranged in the module itself,possibly in direct integration with the stepping motor 38. The motordrive unit 39 is connected by means of a plug and socket connection 40to the program-controlled control unit 35 which, as indicated by outputs41, may be common to stepping motors in a number of different processingstations.

In a manner known per se, the stepping motor 38 is provided with anumber, for instance four, pulse operated windings which may be actuatedfrom the motor drive unit 39 so as to cause the stepping motor toperform a certain angular turn, for instance 1.8° or 3.6°, in one or theother direction of revolution dependent on the switching configurationof the drive windings, not illustrated, at each supplied drive pulse.Thus, the number of revolutions or the angular turn performed in a givenoperational phase for the stepping motor will be determined by thenumber of pulses, whereas their separation or the pulse frequency willdetermine the velocity and acceleration in the rotation of the steppingmotor and the pulse power, i.e. the product of pulse height and width,will determine the torque.

Thus, by controlling the supply of drive pulses from the motor driveunit 39 to the stepping motor 38, an arbitrary desired movement functionof the stepping motor 38 and, thereby, of the member driven by it, inthis case the roller 19, may be realized in practice.

In FIGS. 4 and 5, an example thereof is illustrated purelyschematically, FIG. 4 showing a movement diagram, for instance for theroller 19, for velocity v as a function of time t. In this example, thecourse of movement illustrated by a curve 42 comprises an accelerationphase 42a succeeded by a rotational phase 42b of constant velocity. Sucha course of movement may be realized by means of a pulse train of theform shown very schematically in FIG. 5, in which the separation of thepulses 43 in a first portion corresponding to the acceleration phase 42ais gradually reduced corresponding to a gradually increased pulsefrequency, after which the pulse separation is kept constant in thesucceeding part of the pulse train corresponding to the rotational phase42b.

The generation of drive pulses in the motor drive unit 39 is actuatedand controlled from the control unit 35 which may comprise a microprocessor provided in a manner known per se with an internal clock unitand a program memory, for instance of the EPROM type. In the programmemory of the micro processor, programmes or subroutines for the actualmovement function to be performed of each of the stepping motorscontrolled by the control unit in the operational phase associatedtherewith within the entire operational sequence are stored in additionto the main program for the entire sequence of operations to beperformed by the processing stations controlled by the control unit.

Each of these subroutines comprises complete information about the pulsetrain to be generated in the motor drive unit 39 for the performance ofthe desired movement function. The motor drive unit 39 comprises a pulsegenerator for generating drive pulses of the pulse power necessary toobtain a desired torque, and a logic circuit which under control by theinformation supplied from the control unit establishes the switchingconfiguration for the windings of the stepping motor corresponding tothe rotation in the desired direction of revolution, on one hand, andsupplies the drive pulses to the stepping motor in a pulse traincomprising the prescribed number of pulses with the prescribed mutualseparation thereof, on the other hand.

For a given machine configuration, the desired movement function for agiven stepping motor in a certain operation phase within an operationalsequence, as well as the drive pulse train from the motor drive unit 39associated therewith and the control information contained in theassociated subroutine in the micro processor will remain unchanged, sothat each subroutine is burned in fixed form into the program memory.

However, the design of the program memory as an EPROM type memory opensa simple and advantageous possibility of reprogramming of any storedmovement function with the possibility resulting therefrom forindividual change of the operational parameters for a single processingstation without interferring with the functions of the remainingprocessing stations.

As a particular embodiment of a processing station, the advancing module17 designed as a sheet feeding unit is shown in FIG. 6.

In the design illustrated, the sheet advancing rollers 19 and 20 and aguide wall 43 cooperating therewith are positioned below a sheet outletopening 44 in the upper wall of a cassette 45 outside a sheet supply 46positioned therein.

For cooperation with one or more underlying cassettes 47, only one ofwhich is shown in FIG. 6, an opening 48 is, furthermore, provided in thebottom wall of the cassette 45 to receive sheets from the cassette 47.

In principle, the cassette 47 is designed in the same way as thecassette 45 in respect of the positions of a sheet collecting roller 49and sheet advancing rollers 50 and 51. However, in this case the guidewall 52 cooperating with the latter rollers have a more rectilinear formfor advancement of sheets from the cassette 47 to the intermediateclearance between rollers 19 and 20 in the cassette 45, the guide wall43 of which is curved to define a sheet advancing path leading to theimage transfer module 16.

In FIG. 7, the drive arrangement for a sheet feeding unit as shown inFIG. 6 is shown at a larger scale. As members which must perform adriven rotational movement and, therefore, be in drive connection withthe stepping motor 38, the collecting roller 18 and the driven advancingroller 19 are provided in this example.

The collecting roller 18, the rotational movement of which forcollecting the upper sheet from the sheet supply 46 shall becounter-clockwise, as shown by an arrow, is connected with a gear 53which engages through a gear transmission comprising two wheels 54 and55 a drive gear 56 connected with the stepping motor 38 through a doupletoothed belt transmission 57, 58.

The driven advancing roller 19, which for the purpose of sheet advancingin the gap between itself and the pressure roller 20 must likewiserotate counter-clockwise, is connected with the drive gear 56 through agear transmission comprising a single wheel 59. As will appear from therotational directions for gears 54, 55 and 59, shown by arrows, thisarrangement entails that in the operational phase for the collectingroller 18, the drive gear 56 must rotate clockwise, and in therotational phase for the driven advancing 19, it must rotatecounter-clockwise, as shown by opposed arrows 18' and 19', respectively.

Thus, the stepping motor must be caused to rotate with oppositedirections of revolution in the two operational phases for the rollers18 and 19 immediately succeeding each other. However, as will appearfrom the above explanation, this may also be realized without difficultyby the described control of the stepping motor 38.

Since the gear 53 connected with the collecting roller 18 is in driveengagement with the drive gear 56 also during the operational phase ofthe roller 19 and is still in frictional engagement with the sheetscollected from the sheet supply 46 in a substantial part of thisoperational phase, the connection between the collecting roller 18 andthe gear 54 is constructed with a free-running mechanism, for instancein the form of a ratchet or spring mechanism allowing rotation of gears54, 55 and drive gear 56 and, thereby, of the stepping motor 38 with theopposite direction relative to that prescribed for the operational phaseof the collecting roller 18 itself. Different driven, for instancerotating members with individual directions of revolution in a givensheet processing unit or module may be operated in different operationalphases during an operational sequence by means of a single steppingmotor. In particular, such a design of the drive arrangement may beadvantageous in processing stations like the illustrated sheet feedingunit having relatively closely positioned members to be operated indifferent phases. If several driven members are to be operated in thesame phase or step in an operational sequence, or if the connection witha common stepping motor will require a relatively complicatedtransmission, it will often be more advantageous to use a stepping motorindividually for each of the driven members.

Although the advantages of the invention will appear to the widestpossible extent in case of an apparatus composed entirely of moduleslike the described information printer, the advantages with respect to amore accurate control will in particular, also be obtainable if asmaller number of sheet processing units are designed in accordance withthe invention including in particular the sheet supply with associatedsheet feeding means, the photoconductor and the sheet advancing deviceconveying sheets onto the fixation device when they are being strippedoff from the photoconductor at the image transfer station.

I claim:
 1. An electrophotographic information printer utilizing azerographic system comprisinga sheet supply with associated sheetfeeding means for feeding individual sheets to a sheet advancing path; amovable photoconductor with an associated image transfer device arrangedat said sheet advancing path for transferring a toner image developed onsaid photoconductor to a sheet advanced along said sheet advancing path;a further sheet advancing device for conveying sheets from said imagetransfer device to a fixation device; said sheet supply device withassociated sheet feeding means, said photoconductor and said furthersheet advancing device forming individual replaceable first, second andthird sheet processing modules, respectively; at least two of saidfirst, second and third modules each including a rotatable member and anindividual drive means in the form of an electronic stepping motor whichis mechanically coupled to the respective rotatable member within saidmodule; a program-controlled control unit; and a device operated by theprogram-controlled control unit for selectively supplying predeterminednumbers of pulses at controlled pulse frequencies to the respectivestepping motors within said at least two modules for operating saidstepping motors in an operational sequence for said information printer.2. A processing station as claimed in claim 1, wherein saidprogram-controlled unit includes an EPROM-device containing storedcontrol information in the form of program routines for a prescribedmovement function for each stepping motor.